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Hello everyone,
I was driving my 1969 Corvette and the transmission was slightly slipping. When i returned I checked the fluid level in the driveway and it was low. I tried to top it off, but wasn't paying close attention and grabbed motor oil by mistake. Same blue plastic container. As soon as I saw the amber color I yanked the funnel right out. I would guess maybe 2 -4 oz of oil.
What should I do now?
Drain it and fill it up?
Should I replace the filter, I did start the car briefly and pull it in the garage.
Or can I just add ATF and forget about it?
There's an awful lot of ATF in there with what the trans holds, the lines and cooler in the rad and the torque converter. 2-4 ozs isn't much.
I'd top it up with ATF, repair the leak and drive on.
There's an awful lot of ATF in there with what the trans holds, the lines and cooler in the rad and the torque converter. 2-4 ozs isn't much.
I'd top it up with ATF, repair the leak and drive on.
Hello everyone,
I was driving my 1969 Corvette and the transmission was slightly slipping. When i returned I checked the fluid level in the driveway and it was low. I tried to top it off, but wasn't paying close attention and grabbed motor oil by mistake. Same blue plastic container. As soon as I saw the amber color I yanked the funnel right out. I would guess maybe 2 -4 oz of oil.
What should I do now?
Drain it and fill it up?
Should I replace the filter, I did start the car briefly and pull it in the garage.
Or can I just add ATF and forget about it?
Thanks for your advice
Tom
Until you've affected a remedy, Do NOT run engine any further.
Pull pan, drain trans, replace trans filter & pan, disconnect (& drain) Both fluid lines from radiator's Passenger Side trans cooler.
Start engine & idle and allow trans fluid to drain until it ceases; just a minute or two. (most fluid will remain in torque converter)
Reconnect trans cooler lines and refill auto trans with correct ATF.
Continue checking lines & pan for any leaks for a week or so. Once purged, trans will probably be just fine.
Think through & practice an improved procedure that'll likely prevent same and/or similar mistakes.
(change ATF brand to one in a bottle of different color than your favorite motor oil's bottle ?)
*While OE steel pan is off, look for an OE magnet "attracted" to inside of pan.
Inspect magnet and clean away any material sticking to it.
So, if a TH400 holds 11-12 quarts of fluid, 11.5 is 368 ounces. 1 percent of that is 3.68 ounces.
Will 1 percent oil in the tranny hurt it? I'd say don't worry about it, but someone may disagree.
"TH400 Transmission Fluid Capacity
For TH400, the amount of transmission fluid it takes is 6 quarts in the pan. You can expect to use between 11 and 12 quarts of fluid in the stock version."
Last edited by zxryder72; Dec 16, 2025 at 08:50 AM.
I've been retired for 11 years now so I don't recall everything right away. So motor oil shouldn't be used in a automatic transmission otherwise your transmission will go boom, right? Well some ZF transmissions that was used in heavy duty class 8 trucks used 15w-40 motor oil. When I first saw the "15w-40 motor oil" tag on the transmission dipstick I said what? Then I put out the stick and sure as hell it was motor oil. Now these weren't automated manuals or any other goofy transmissions. They were straight up wet clutch, (Homer) Simpson planetary gear, torque converter transmission just like a Turbo 400, just bigger. So don't even give it a second thought.
"Well some ZF transmissions that was used in heavy duty class 8 trucks used 15w-40 motor oil."
WELL...no wonder my Tacoma 5 speed A.T. would bark the tire in 2nd gear!
My PTSD let me pour 4 qts. of 10w-20wt. toyota engine oil into my trans when I changed the fluid 3 years ago.
I may bring back the red trans fluid and get 4 more qts of 10-20wt! I change the fluid every 30,000 miles...its an aviation thing.
If a transmission is designed to use ATF, and its manufacturer specifies ATF, you should use what the manufacturer specifies. No matter if trans is auto or manual; use what the manufacturer specifies.
There are Very Few certified tribologists on this planet; and fewer yet on car forums. Your transmission, your money.
I wouldn’t worry if you only added a few ounces like you stated.
If it makes you feel better, drain the pan, and refill with the proper fluid.
I would only drop the pan and replace the filter if you want to replace it and need to service the transmission.
With only a few ounces it’s unlikely you caused immediate damage, but since it was already slipping I wouldn’t ignore it. The safest move is to drain the pan, replace the filter, and refill with the correct ATF so you know the mix is right. Simply topping off might work, but given the symptoms you had before, a service now is cheap insurance.
Do you think a transmission shop is going to give you at honest answer especially this time of the year?
Well, I didn't say transmission shop -- or at least I didn't intend to. I was thinking the shop that you trust to work on your daily drivers, the shop that wants your trust and continued business.
Thanks, everyone, for the advice.
I have given this a lot of thought, and I have decided to drain the fluid and replace the fluid. It was my dad's car, and I would be so disappointed in myself if I destroyed the transmission.
Because I only started it for a few seconds and drove it a couple of feet further in the garage, I think flushing the lines won't be necessary.
But Rebelyell is completely right, I should have been paying more attention, a good lesson to slow down
The fluid was low due to a leaking vacuum modulator, which I am (pretty) confident I have resolved.
Following.
Transmission fluid mishap
